1. Field of the Invention
The present invention relates to a sheet feeding apparatus for a corrugated fiberboard container making machine for feeding stacked corrugated fiberboard sheets one after another.
2. Description of Related Art
FIGS. 8 and 9 are explanatory views showing outlines of conventional sheet feeding apparatuses for a corrugated fiberboard container. In FIG. 8, frames 1 are erected on both sides, right and left, of a table 2, and a beam 3 is installed between the frames 1. A hopper 6 is defined by front stops 4 attached to the beam 3 and side guides 5, and corrugated fiberboard sheets 7 are stacked on the table in this hopper 6. A lowermost sheet 7a of the stacked corrugated fiberboard sheets 7 is kicked from one end side by a kicker 8 and reaches feed rolls 9 on the other end side as indicated by the chain line. Then, the sheet 7a is pulled by the feed rolls 9 and is sent to the following process (for example, a printing section 10).
FIG. 9 shows an outline of a sheet feeding apparatus of another type. In this sheet feeding apparatus, delivery rolls 11 are provided under the front stops 4 in place of the kicker 8, and the vacuum pressure in a vacuum box (suction box) 12 attracts the lowermost sheet 7a to the surface of the delivery rolls 11, so that the sheet 7a is delivered by a frictional force.
The above-described conventional sheet feeding apparatuses for a corrugated fiberboard box making machine have problems as described below. For example, if the feed roll 9 wears eccentrically, the feeding force becomes nonuniform in the transverse direction. Also, in the case shown in FIG. 9, if the corrugated fiberboard sheet 7 is warped, the contact pressure between the delivery roll 11 and the lowermost sheet 7a of the corrugated fiberboard sheets 7 becomes nonuniform in the transverse direction even with the aid of the suction pressure of the vacuum box 12. Particularly for a corrugated fiberboard sheet with high flexural rigidity such as a double-sided sheet, such tendency is remarkable.
Thus, when a feeding force that is nonuniform in the transverse direction is applied to the corrugated fiberboard sheet 7 under the mechanical condition of eccentric wear of the feed roll 9 or under the condition of warped sheet 7, the sheet 7 is fed while being turned obliquely at a predetermined angle as shown in FIG. 10. The sheet 7 fed in this manner decreases the accuracy of box made in the subsequent process. Therefore, the accuracy is kept by a correction, for example, by decreasing the sheet feed speed or by purposely installing the kicker 8 slantwise.
Since such a tendency for oblique turning is often developed by the eccentric wear of the feed roll 9, the warping of the corrugated fiberboard sheet 7, and the like as described above, the oblique turning does not occur at random for each corrugated fiberboard sheet 7, but there is a tendency for all corrugated fiberboard sheets 7 of a certain production lot to be turned obliquely in the same manner.